powerpc/85xx/86xx: some refactoring for fsl_uli1575 code

- Get rid of uses_fsl_uli_m1575, it does not scale for all cases.
  Instead, let's explicitly use machine_is() for each fixup.
- Factor out MPC8610HPCD quirks to fsl_uli1575, and protect them with
  machine_is(). One step closer to multiplatform kernels.
- Actually use fsl_uli1575 on MPC8610HPCD, so RTC quirk will be applied.
- RTC quirk applies to all boards though, so no machine_is() checks.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>